Process of oxidizing ammonia to nitric acid



A. HENWOOD. PROCESS OF OXIDIZING AMMONIA T0 NITRIC ACID.

APPLICATION FILED JAN. 9, 1919.

Patented July 20, 1920.

M/VE/YTOPI firazam z nwvod ATENT oFr ci-s.

ABRAHAM nnnwoon,

OF CYNWYD, PENNSYLVANIA.

PROCESS OF OXIDIZING AMIVIONIA TO NITRIC ACID.

To all whom it may concern:

Be it known that I, ABRAHAM HnNwoon, a citizen of the United States, residing at Cynwyd, county of Montgomery, and State of Pennsylvania, have invented a new and useful Improvement in Processes of Oxidizing Ammonia to Nitric Acid, of which the following is a full, clear, and exact description, reference being had to the accompanying drawing, which forms a part of this specification.

he purpose oil my invention is to secure a maximum yield of nitric acid of maximum concentration from the oxidation of ammonia gas.

In an application filed by me July 11, 1917, Serial No. 179,804, for process of the oxidation of ammonia to nitric acid, I have set forth a process wherein ammonia gas and oxygen are passed over a catalyxer while maintaining a partial pressure of oxygen equal to or greater than twice the partial pressure of the ammonia gas and forming the majority, and preferably at least two-- thirds, of the total gas pressure, the pressure being suflicient to promote rapid reaction but insutlicient to cause excessive heating of the catalytic body or to cause heating to a point detrimental to the formation of nitric acid. The said application also sets forth other features of novelty, some of which are not therein claimed.

While said application, Serial No. [79,804, discloses the subject-matter herein claimed, the present application is more properly a division oi an application filed by my July 8, 1918, Serial No. 243,758, wherein not only is the same process described, but the same apparatus is used to carry out the process.

The invention herein set forth comprises a process involving the passage oi ammonia gas and oxygen over a catalyzer wherein the. proper temperature at the point of reaction is maintained by cooling by one means, preterably by gas control, and specifically by excess of oxygen, to a temperature near the lower part of the permissible range of term peratures, and correcting for excess of reduction of temperature, and thereby securing the ideal temperature desired, by heat ing by another means, preferably by outside automatically acting thermostatically-controlled electrical means, whereby the temperature of reaction ,may be at all times Specification of Letters Patent.

to permit any Patented July 20, 1920,

,758. Divided and this application filed January 9 No. 270,409.

maintained with the range high enough to secure maximum concentration of nitric acid but not sufiicient-ly high substantial decomposition oi nitric acid.

In my said application Serial No. 179,804, I have explaineiil that the temperature can be regulated entirely by the use of excess oxygen and adjustment of the quantity of excess for selected tube size and quantity of catalyzer, readily determinable by experi ment, or by varying the gas speed, reducing the quantity of gas and, as a consequence, reducing its pressure to reduce its temperature. The present invention does not comprehend the regulation of temperaturc solely by gas control, but contmnplates the lowering and raising oi the temperatin-e by respectively different agencies, the method of lowering the tcmlu raturc by gas control, describml in said application, being" supplemented by an outside, automatic, and preferably thermostatically-controlled and electrical means, to prevent the dropping of the temperature below the minimum range oi ciliciency.

in said application, Serial No. 179,801, and also more specifically in said ap lication filed Ju y S, 190%, Serial No. 243,758, of which. this application is a division, I have described the passage of the gases through a specific type of catalyzer which is especially adaptable to the oxidation ot ammonia to nitric acid. This process forms the subject-matter oi the claims of said application Serial No. 243,75H, and while it is not herein claimed, still the process oi the. present application.operates with the highest degree oi eiiiciclmy and economy it this special improved type ol' catalyzcr be employed and l therefore herein generally describe the same in connection with the description oi the thermostatically-i-ontrollwl electrical heating means employed in connection there with.

The successful employment of this improved catalyzer seems to be dependent upon supporting it in such manner as to avoid impairment or destruction ol its el ficieney. While this ieature ol' the complete process is specifically set forth and claimed in a separate application aerial No. 270, 1] 0, filed January 5), 191i), which is also a division of said application Serial No. 24:3,758, l have deemed it advisable to here of temperaturecomprises a continuous porous or permeable contact or reaction surface, or diaphragm, of catalytic material, preferably platinum sponge, the mass of catalytic material being so small as not to be self-sustainin but distributed uniformly over the suriace of a pcrous or permeable material which is preferably non-metallic, non-catalytic, and a poor conductor of heat.

A base or support of such material of any suitable shape, so covered with a coating, film or diaphragm of platinum, is

laced in the channel provided for the reacion gases so that the latter must pass over or through the same and hence be brought into reactive contact with the continuous surface ofplatinum. Thus I attain maximum economy, even distribution, minimum mass and uniform temperature, and insure that practically every molecule of the reaction gases will be subjected, and in the same degree, to the influence of the catalyzer.

In preparing the catalyzer, l take a support, which may be in the shape of a disk, hemisphere, tube, or any other shape, made of porous orpermeable material, such as alundum or silica. The catalytic material, preferably platinum, is deposited, formed or placed, on either or bothsurfaces of the support, but preferably only on one surface. The catalytic material may be applied in various ways, but I prefer to soak an alundum support in ammonium chlorid, dry it, remove any excess from the surface, spray upon the surface a platinum chlorid solution, thereby forming on the surface a precipitate of ammonium chlorplatinate, and

then dry and ignite, thus burning off or volatizing ammonia, hydrogen chlorid, steam and chlorin, and leaving a superficial layer of platinum sponge. I

To prevent cracking of the support due to expansion and contraction resulting from variation of temperature at the beginning-and end of a run, the edge of the support may be sustained in a groove containing a plastic lute, composed of a vitreous substance of the proper degree of viscosity at the working temperature, and which is chemically inert to the reaction gases, thereby providing an hermetical seal which allows the support to expand as it is heated and contract as it is cooled. I prefer to use a sustaining seal or lute composed of boric acid. a

To secure a fine and certain adjustment of the temperature, which is the subject of the iores'ent invention, I use, as hereinbefore stated, sulficient excess oxygen, or, less desirably, sufiiciently reduce the gas speed, so that the temperature will tend to border on, or even sink below, the lower limit of the range of permissible temperatures, and then add heat from outside, by automaticallycontrolled, and preferably thermostaticallycontrolled, means to maintain the temperature safely above the lower limit of the range of permissible temperatures, thereby offsetting what would otherwise be objec-- tionable depressions of temperature below that at which the reaction takes place advantageously. The heating may be effected by a resistance wire winding arranged in an electric circuit and in proximity to the catalyzer and also to a thermostatic element which is connected to, and operates, a rheostat controlling t flow of electric current, so as to cut out .esistance as the'tempera- .ture decreases and introduce resistance as as to permit the effective execution of the process. The annexed drawing, therefore must be considered as merely illustrative of one of the different ways available for practising the process. The figure is a diagram of that part of the apparatus which may be conveniently called the reaction chztmbenincluding the thermostatically-controlled outside heating means.

In the figure, a and b are two sections of a tube or chamber into which thegases of reaction pass and combine to form nitric.

acid. The tube, at the junction ofthe two sections, is bent circumferentiallyto form a circumferential groove 0 containing boric acid (1 or some equivalent substance that is plastic, vitreous, viscous and chemically inert to the gases. The disk-shaped support 6 composed (say) of silica, holding distributed over its surface, in a continuous manner, platinum sponge f, has a depending peripheral flange g resting in the groove 0 and embedded in the plas tic lute (Z, which, while providing an hermetical seal, allows the disk 6 to expand and contract. The support is either inherently porous or is pro- ,.vided with perforations which permit the free flow therethrough of gas and acid. It

into nitric'acid which consists A resistance wire winding h incloses the- .11, is controlled. A switch 0 provides for opening the circuit when automatic operation is not desired or required.

I do not herein claim the catalyzer, or the combined catalyzer and support therefor, or-the means for retaining the support in position and at the same tlme permitting it to expand or contract, or the process of catalytically combining oxygen and am monia gas to form nitric acid by passing the mixture through said catalyzer or, while so doing, supporting the catalyzer carrier flexibly to provide for its expansion and contraction. These inventions form the subject-matter of separate applications, namely: Serial No. 243,758, filed July 8, 1918; SerialNo. 241,724, filed June 25, 1918; and Serial No. 270,410, filed January 9, 1919. w

Having now fully described my invention, what I claim and desire to protect by Letters Patent is:

1.- The method of keeping down the temperature in the oxidation of ammonia gas in providing for a non-automatic temperature reduction and correcting for excess of reduction by an automatic addition of heat as the lower range of permissible temperature is approached.

2. The method of maintaining theproper temperature at the point of reaction in oxidation of ammonia gas into nitric acid which consists in providing for a normal low temperature for the reaction and automatically heating by outside thermostatically-controlled means when the temperature falls below the designed point.

3. The method or" maintaining the proper temperature at the point of reaction in oxidation of ammonia gas into nitric acid which consists in cooling the gases at the point'of reaction by gaseous means to a point inthe lower part of the range of permissible temperature and protecting from excessively low temperatures by thermostaticallycontrolled outside means.

4. The method of maintaining the proper temperature at the point of reaction in oxidation of ammonia gas into nitric acid which consists in cooling at the point of reaction by excess of oxygen to a temperature near the lower part of the permissible range of temperatures and adding heat by thermostatically-controlled electrical means when the temperature approaches too closely to the lower limit.

In testimony of which invention I have hereunto set my hand at Cynwyd on this 26th day of December, 1918.

ABRAHAM nnnwooo. 

